In recent times, various oxide superconductors have increasingly been discovered which show very high values of the critical temperature (Tc) at which the transition from a normal conductive sate to a superconductive state takes place. Since such an oxide superconductor shows a higher critical temperature than conventional alloy or intermetallic compound superconductors, it is considered that oxide superconductors will highly promise for practical superconducting materials.
However, this sort of superconductor is made of ceramics and is thus very brittle, cracks being easily produced. We have attempted the production of various superconducting wires each comprising an oxide superconductor as the conducting portion, in which a metal sheath was charged with an oxide superconducting material in a powder form, and the oxide superconductor charged metal sheath was then subjected to diameter reduction and then to heat treatment.
In the above-described method, however, the oxide superconducting material powder is contact with the metal sheath which contains an oxidizing metal such as copper, a copper alloy, or stainless steel, during the heat treatment, in which this oxidizing metal takes oxygen away from the superconducting material and is oxidized. As a result, the contact portions between the superconducting material powder and the oxidizing metal lacks oxygen. Consequently, a problem occurs in reductions both in the critical temperature and in the critical current density of the product superconductor.